The present invention relates generally to a continuous in-line compounding and extrusion system, and more particularly to, a continuous in-line compounding and extrusion system that produces net shapes. The present invention is useful for several different formulations and material composites including, but not limited to, polyvinyl chloride (PVC) formulations, polyethylene (HDPE) formulations, and cellulosic/polymer composites. The present invention will be described primarily with reference to cellulosic/polymer composites, but it is also intended for use with other material composites and formulations.
Cellulosic/polymer composites are used as replacements for all-natural wood, particle board, wafer board, and other similar materials. In recent years, a tremendous demand has developed for cellulosic/polymer composites that exhibit the look and feel of natural woods. Unfortunately, the supply of natural woods for construction and other purposes is dwindling. Consequently, many are concerned about conserving the world""s forests, and the cost of natural woods has risen.
The demand for cellulosic/polymer composites has also increased for other reasons. As compared to natural woods, cellulosic/polymer composites offer superior resistance to wear and tear. In particular, cellulosic/polymer composites have enhanced resistance to moisture. In fact, it is well known that the retention of moisture is a primary cause of the warping, splintering, and discoloration of natural woods. Moreover, cellulosic/polymer composites may be sawed, sanded, shaped, turned, fastened, and finished in the same manner as natural woods. Therefore, cellulosic/polymer composites are commonly used for applications such as interior and exterior decorative house moldings, picture frames, furniture, porch decks, window moldings, window components, door components, and roofing structures.
Traditionally, two types of processes have been employed to manufacture cellulosic/polymer composites. The first type of process manufactures the cellulosic/polymer composite materials into pelletized feed stock that is later, at another site, fed into a single or twin-screw extruder. The output of the extruder is then sent through a profile die to obtain a net shape. However, this type of manufacturing process has drawbacks because it requires an independent mixing and storage system to compound, pelletize, cool, package, and store feed stock of the cellulosic/polymer composite materials.
The second type of manufacturing process eliminates the need to pelletize, cool, package, and store feed stock of the cellulosic/polymer composite materials. Instead, the second type of manufacturing process blends the polymer materials into a homogeneous mixture. The homogeneous mixture is delivered to a site where it is then combined with pre-dried wood flour. The resulting composition is fed through a twin-screw extruder which converts the composition into a fused melt. The fused melt is then pumped through a profile die to achieve a net shape.
Conventional use of a twin-screw extruder, however, is not an efficient means to maintain a relatively dry mixture. Moreover, when employing the second type of manufacturing process, precise guidelines must be adhered to in order to achieve the superior qualities of cellulosic/polymer composites. Most importantly, the wood flour that constitutes the cellulosic material must be dried before it is extruded. As is well known in the art, failure to dry the wood flour before it is extruded will commonly result in a fragile composite that is susceptible to cracking, blistering, and deteriorating appearance.
Once the wood flour is dried to the appropriate moisture content level for the second type of manufacturing process, care must also be taken to prevent the wood flour from reabsorbing additional moisture before it is extruded. Early attempts at manufacturing cellulosic/polymer composites failed because the wood flour was stored in humid manufacturing environments before it was extruded. Compounding systems for the second type of manufacturing process have since been employed to prevent the wood flour from absorbing undesired moisture. One such system utilizes a large dryer to pre-dry the wood flour and to maintain a dry storage environment for the wood flour.
Cost is an inherent drawback to using a large dryer to pre-dry the wood flour or to maintain a dry storage environment for the wood flour. For example, a drying/blending system for a large scale production facility can cost several million dollars. In addition, this type of compounding system requires bulky storage containers to hold the cellulosic/polymer composite materials, an elaborate piping and control system to transfer the cellulosic/polymer composite materials to various holding stations, and an independent mixing mechanism to combine the cellulosic/polymer composite materials. Consequently, such a compounding system is costly, susceptible to wear and tear, and time-consuming.
On the other hand, a compounding system which utilizes pre-dried wood flour that has been purchased from a remote commercial compounder also has shortcomings. The extra cost of dealing with a remote commercial compounder is not desirable, and the wood flour may have to be redried once it arrives at the extrusion facility prior to passing it through the extruder. This approach also has inherent drawbacks such as ordering, shipping, and material handling problems. Therefore, regardless of the compounding system which is employed, the second type of manufacturing process also possesses undesirable characteristics.
In light of the deficiencies of known manufacturing processes, a need exists for a manufacturing system that does not require an independent mixing mechanism to pelletize, cool, package, or store feed stock of the cellulosic/polymer composite materials. In addition, a need exists for a manufacturing system that utilizes a compounder instead of a twin-screw extruder to blend the cellulosic/polymer composite materials into a composite melt, and a need exists for a manufacturing system that does not require a costly, large dryer to pre-dry the wood flour or to maintain a dry storage environment for the wood flour. The present invention is designed to address these needs. The present invention is also designed to produce net shapes at higher rates, to streamline the manufacturing process, to create a manufacturing system that is less susceptible to wear and tear, to reduce the production costs of wood flour, to eliminate the drawbacks of independent drying, blending, and pelletizing systems, and to eliminate the problems caused by the shipping and material handling of wood flour.
In particular, the present invention continuously produces net shapes via an automated and continuous compounding plus finish extrusion system that does not require pre-dried wood flour or pelletized feed stock of the cellulosic/polymer composite materials. An exemplary embodiment of the present invention utilizes automated loss-in-weight feeders to dispense wood flour and all of the other cellulosic/polymer composite materials into a compounder. The compounder blends the cellulosic/polymer composite materials into a composite melt. The composite melt is continuously devolitalized as it travels through the compounder, a transition chute, and a finish extruder. The composite melt is then forced through a profile die which is fitted to the finish extruder in order to achieve a net shape.
The present invention, however, is not limited to the production of cellulosic/polymer composite shapes. The present invention may also be utilized to produce net shapes from material composites or formulations that do not include cellulosic materials. For instance, the present invention may produce net shapes from polyethylene (HDPE), polyvinyl chloride (PVC), and formulations that incorporate these materials. Moreover, the present invention may be used in conjunction with any material that may be adapted to be formed into a net extruded shape.
In addition to the novel features and advantages mentioned above, other objects and advantages of the present invention will be readily apparent from the following descriptions of the drawings and exemplary embodiments.